docs: def url(self):
          """
          This attribute retrieve the url that will be used as a HTTP request to
          the Crossref API.
  
          This attribute can be used compounded with query, filter,
          sort, order and facet methods.
  
          Examples:
              >>> from crossref.restful import Works
              >>> Works().query('zika').url
              'https://api.crossref.org/works?query=zika'
              >>> Works().query('zika').filter(prefix='10.1590').url
              'https://api.crossref.org/works?query=zika&filter=prefix%3A10.1590'
              >>> Works().query('zika').filter(prefix='10.1590').sort('published').order('desc').url
              'https://api.crossref.org/works?sort=published&order=desc&query=zika&filter=prefix%3A10.1590'
              >>> Works().query('zika').filter(prefix='10.1590').sort('published').order('desc').filter(has_abstract='true').query(author='Marli').url
              'https://api.crossref.org/works?sort=published&filter=prefix%3A10.1590%2Chas-abstract%3Atrue&query=zika&order=desc&query.author=Marli'
          """
          request_params = self._escaped_pagging()
  
          sorted_request_params = sorted([(k, v) for k, v in request_params.items()])
          req = requests.Request(
              'get', self.request_url, params=sorted_request_params).prepare()
  
          return req.url